Decimeter radio wave propagation in the turbulent plasma near the sun, using Venera 10 spacecraft

Abstract

The 1976 Venus superior solar conjunction resulted in the occultation of the spacecraft Venera 10 by the sun at solar minimum. At the conjunction time, decimeter radio waves passed through the solar corona. The broadening of the spectrum line, as well as amplitude and frequency fluctuations, was observed over extensive distances of the radio link from the sun. The fluctuation characteristics of the radio waves are used to determine solar wind parameters. The fluctuations of the electron concentration have been shown to decrease rapidly with the increasing distance from the sun, but in the region between 12 and 20 solar radii (Rs) the irregularities have increased values. The shape of the spatial spectrum is closely described by the power function ΦN(q) ∝ q−p, but the spectral index may have different values in different parts of the spectrum. The spectral index of the small‐scale part of the spectrum decreases with the decreasing distance from the sun, and at radial distances shorter than 12 Rs its value is close to 3.0 ± 0.2. The inner scale of turbulence of the near‐sun plasma is of the order of several kilometers at distances between 6 and 10 Rs. Typical values of the velocity of motion of the inhomogeneities are 30–40 km/s at radial distances from 2 to 6 Rs, while at distances greater than 18 Rs the velocity exceeds 400 km/s.